Pneumatic conveying system



Sept 7 1954 N. o. KRENKE 2,688,518

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Patented Sept. 7, 1954 UNITED STATES PATENT GFFICE PNEUMATIC CONVEYING SYSTEM tion ofNew York Application August27, 1952, Serial N o. 306,696

(Cl. .BOZ- 28) v12 Claims. 1

The present invention relates to pneumatic conveying systems and constitu-tes an improvement on the type of conveying system for flour and' similar materials disclosed in the copending application of Albert O. Riordan, Serial No. V291,837 viiled June v5, 1952.

In the system disclosed in the above-mentioned Riordan application, il'our or other similar material may be conveyed vfrom a bin or other starting point through a `main pneumatic conveying conduit to any one of a plurality of hoppers, in which the product is weighed. Themain-cond-uit is in the form of a closed loop which returns to `the bin; and each of the scale hoppers may be Vconnected'to the conveyor by a diverter valve in themain conveying conduit. When a scale hopper receives the desired quanti-ty of flour, the diverter valve is shifted to its straight-through position and the feed of our to the inlet end of the conveyor conduit is terminated, but the flow of conveying air is continued for the purpose of returning any llour in the conduit to the bin through the return loop. The air discharged from the hopper is exhausted through Va specia-l dust-collecting conduit. One advantageof the Riordan system lies in the fact that it is not necessary to provide a highly efficient separator at the destination, since failure of the separator to eiect a complete separation of lflour and air will Vnot introduce any errors in the weighed quantity vdelivered to the hopper.

It is one of the objects of the present invention to improve and simplify the above-'described Riordan system by `eliminating the dust-collecting conduit and associated suction `pumps and dust separators, which are costly and occupy considerable space.

Another object isto provide a conveying system in which there is even less need for complete separation of flour and air at the scale hopper than -is =thelcase in the Riordan system.

Other objects and advantages of the'invention will become apparent from thefollowing specification, the accompanying drawings, and the appended claims.

'In the drawings:

Figure 1 is va-diagrammatic view of a relatively simple example of the improved conveying system in which means are provided for selectively-delivering yflour to either one `of two scale hoppers;

Figure 2 is a fragmentary view of a modication of the system shown in Figure l; and

Figure 3 is an enlarged sectional view lofthe diverter-valveemployed in the modified'system of Figure 2.

Cil!

' the iilter Il.

The system illustrated in Figure 1 includes a single storage bin, means for loading the bin, and means for discharging flour from the bin to either one of two mixers. In loading the bin, flour from sacks or yany other source is dumped into a blender I, `from which it is conveyed to the storage bin-2 From this bin, flour may be conveyed selectively to either one of a pair of flour scales 3 and 4 mounted, respectively, over dough mixers 5 ands. Suitable shut-oil valves 1 and 8 are provided between the weighing scales and the mixers for use in discharging the contents of the scales into the mixers after the desired quantity of flour has been delivered.

The conveying system for bin loading includes a positive displacement compressor or blower 9, which preferably is of the Roots type and which supplies air under pressure to a three-way valve -I 0, which is 'adjustable between two positions.

For bin loading, the valve I@ is so adjusted that it connects the blower to a conveying conduit II, -which supplies air to a motor-driven paddlewheel typefeeder I2, vwhich delivers flour to the current of air flowing between the conduit II and the feeder discharge conduit I3: Any suitable form of feeder may be employed for this purpose, -suitable types being disclosed, for example, in lthe patents to Rieth No. '717,926 and Colburn No. V2,550,781. The flouris conveyed by the air current through the conduit I3 and discharges tangentially into an air separator I4, which is simply a relatively low cylindrical housing having a coverplate. The bottom of the cylindrical housing is open and permits the flour to fall by gravity into a motor-driven sifter I5, which is positioned on top of the storage bin and discharges the sifted flour by gravity into the bin. The storage -bin preferably is provided with a motor-driven leveling bar of conventional construction. This bar, which is not illustrated in the drawings, is rotatable on a vertical axis and is positioned near the top of the bin, so that it will distribute yflour evenly and per-mit complete filling of the bin.

In order to collect and remove fine dust which results from the emptying of flour sacks in the blender I, there is provided a small, motor-driven centrifugal Aseparator IB, preferably of the type known in the trade as a Roto-Clone separator. The separator IB discharges into an air filter I1. The separator I6 acts as a suction fan, drawing air from the blender through conduit I8 and discharging air from which most of the entrained flour has been removed through a conduit I9 to Thus, the flour removed from the t 3 air drawn from the blender through conduit |8 is collected in part in a collection chamber in the separator I6 and in part in the air lter When it is desired to discharge flour from bin 2 to either of the scale hoppers, the three-Way valve ||l is shifted to connect the motor-driven blower 9 to the conduit 2|, which supplies air under pressure to a bin discharge feederv 22, similar in construction to the previously described feeder I2. The flour-laden air leaves the feeder 22 through a main conveying conduit 23, which extends past and closely adjacent to the ilour scales 3 and il. A pair of three-Way valves 24 and 25 is provided in the conduit 23 adjacent the scale hoppers 3 and il, and the valves operate in one position to connect the main conduit 23 to branch conduits 29 and 33, respectively. Branch conduit 29 discharges tangentially into a separator 3U, similar in construction to the previously described separator i6 except that its coverplate is provided with an axial air discharge opening to which is connected a discharge conduit 3| containing a check valve 32. The discharge conduit is connected to the main conveying conduit and, consequently, the air from the separator 30 is returned to the main conduit, through which it flows to the storage bin 2. The check valve 32 may be of conventional construction, and preferably is simply a nap-type valve which permits ow from the separator 3i] to the main conduit 25 but blocks fiow in the opposite direction.

The branch conduit 33 discharges tangentially into a similar separator 34 positioned on top of the scale il. The outlet from the separator 31S likewise is connected to the main conveying conduit 2 by a conduit 35 containing a check valve 3S which operates to block flow from the main conduit through the conduit 35 to the separator 34. The branch conduits 29 and 33 and the air discharge conduits 3| and 35 preferably are made of iiexible material, so that they will not interfere with the operation of the weighing scales. The return main iconveying conduit 2l' is connected to a separator 28 mounted on top of the storage bin 2, the construction of separator 28 being identical to that of separator Ill.

It will be observed that the system abovedescribed differs from that of the previously mentioned Riordan system in that the separators 30 and 33 at the scale hoppers have their air discharge outlets connected directly to the return loop of the main conveying conduit, instead of being connected to a separate dust-collecting suction lconduit which, in turn, must be connected to a relatively large centrifugal separator and i filter similar to the small separator and filter l and previously described. The system also differs in that neither the storage bin nor the separators lli and 28 on the storage bin have air discharge outlets connected to a dust-collecting system; but, in lieu thereof, air is discharged through a lter into the atmosphere. This filter is mounted on the bin, itself; but, if desired, separate lter outlets could be provided on each separator. As a result of these changes, it will be noted that all portions of the system of the present invention operate under a positive air pressure; i. e., the scale hoppers, the separators 311 and 34, the air discharge conduits 3| and 35, the return loop 2l' and the storage bin 2 all are under a positive air pressure supplied by the blower 9, and the air delivered by the blower not only delivers flour from the storage bin to the diverter valves 24 and 23 but also operates to return to the storage bin any residual flour not separated from the conveying air by the separators 30 and 34.

The use of a blower at the air inlet end of the conveyer permits the use of a blower of smaller volumetric capacity, smaller tubing and a higher ratio of flour to air, all of which are advantageous. However, many of the advantages of the invention may be realized by positioning the blower on the air outlet from the bin, thus operating the system as a suction system. In that case, valve Il) may be replaced by a pair of shut-olf valves, one each for conduits i and 2|, which will open these conduits to atmosphere.

After the delivery of flour to either of the scale hoppers is completed and the diverter valve associated with that scale hopper is returned to its straight-through position, the operation of the feeder 22 is stopped and the blower 9 continues to blow air through the main conveyer conduit until all flour therein is cleared. Thus, each delivery operation starts with conduits completely cleared of flour. It will be noted that it is unnecessary for the separators 3|] and 34 to effect complete separation of air and our because only the separated flour is weighed and any unseparated our which is discharged through conduits 3| and 35 is simply returned to the storage bin. As a result, the separators may be of very simple and rudimentary construction low in cost, and, therefore, may occupy very little space or headroom.

Except as above indicated, all of the elements of the system disclosed in Figure l may be identical to the corresponding elements in the system disclosed in Figure l of the aforementioned Riordan application. Moreover, the automatic electrical control circuit disclosed in Figure 3 of said Riordan application may be employed to operate the system of the present application. The only change which need be made in the control circuit of the Riordan application is to eliminate those portions of the circuit relating to the Roto-Clone separator, in which event the Roto-Clone separator i@ of the present invention may be manually started and stopped independently of the main electrical control circuit.

In Figure 2 is illustrated fragmentarily a modied form of the invention, in which a single composite valve is employed in lieu of the diverter Valve and the check valve associated with each scale hopper. Only that portion of the system associated with one of the scale hoppers is illustrated, but it will be understood that the mechanism associated with each scale hopper will be similar and that the remaining portions of the system will be the same as those illustrated in Figure l. Thus, as shown in Figure 2, the main conveying conduit 23-25 has positioned therein a diverter valve 43. The branch conduit 29, which delivers our and air to the separator 30 on scale 3, also is connected to the diverter valve 50, as is the air discharge conduit 3|, which extends from the separator 30 to the valve. As hereinafter set forth, the construction of valve 49 is such that in one position it connects the main conveynig conduit sections 23--25 and blocks the branch conduit 29 and the air discharge conduit 3|. In its other position, valve 4l) connects the main conduit section 23 to the branch conduit 29 and at the same time connects the air discharge conduit 3| to the main conveyer conduit section 25, thus diverting flour and air to the separator 3d and returning the air discharged from the separator to the main conveying conduit at a point beyond the valve.

aoeegers -Ihe construction of valve `40y is illustrated in greater detail in Figure 3. As there shown, the valve comprises a stationary housing 4I having a pair of discharge ports 42 and 43, the discharge port 42 being yconnected to the main conveying conduit section 25 and the discharge port 43 kbeing connected to the flexible branch conduit 29. The housing 4l is generally in the form of a cylinder extending at right angles to the port 42'.. A generally cylindrical valve element 44 is slidable within the cylindrical housing and is .equipped with a pair of pistons 45 and 46, by means' vof which it may be actuated. The ends ofthe cylinder 4I are closed by cylinder heads 4l and 4-8 equipped with air control conduits 49 and .50, through which air under .pressure may `be supplied or discharged for the purpose of shift- .ing the valve element 44 from one end of the cylinder to the other. The conduits 49 and 50 .may be controlled by any conventional form of four-way air valve, preferably a solenoid-operated Yvalve* of the type described in the aforementioned Riordan application for operating the dil-vertervalves therein disclosed.

The movable valve element 44 has .a pair of ports l and 52 extending therethrough. A flexible ysection of the main conveying conduit 23 Vis connected to the port 5I by means of a sleeve 53; and the flexible .air return conduit 3l is connected bymeans of va sleeve 54 to the port 52. The wall of the valve housing 4l is provided with an opening v55 at one side to permit movement of the sleeves `53 and-54 and associated conduits axially Awith reference to the valve housing.

It -will be observed that when the parts are in the `position shown in Figure 3, the port 5l in the valve element 44 connects the main conveying conduit 23 to the main conveying conduit section 25 and blocks the branch conduit 29 and the air discharge conduit 3 l. However, when air under pressure is supplied through the pipe line 501and air is exhausted from pipe 49, the valve element will shift downwardly, as viewed in Figure '3, thus placing port 5I in communication with port-43 of the valve housing and at the same time placing port 52 in communication with port 42 of the Valve housing. In that position, therefore, flour and air entering from the main conduit section 23 iiow into the branch conduit 29 and the air discharging through conduit 3l returns tothe main conveying conduit section 25. It will be observed that valve thus performs the combined functions of the valves 24 and 32 in the form of invention shown in Figure 1. Consequently, no check valve is required in the air discharge conduit.

While vonly two forms of the invention are illustrated and described, it will be understood that other variations in the principles of the systems herein disclosed may be indulged in without departing from the spirit of the invention or the scope of the appended claims. Thus, for example, the application of Applicants improvement to the ybasic closed loop system of the aforementioned Riordan application may be employed in any form of system embodying a main conveying conduit in the form of a closed loop, regardless of the number of starting points or storage bins and regardless of the number of destinations or scale hoppers.

'What is claimed is:

`1. A pneumatic conveying system for delivering `bulk'nour or like material from a container to a `remote destination, including a container from which the material may be drawn, a receptacle at the remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacle in close proximity thereto and returning to -the container at its discharge end, means including a diverter valve in the main conduit adjacent the receptacle operative when the valve is in its diverting position to divert material from `the main conduit into the receptacle and in its :straight-through position to block communication between the main conduit and the receptacle and permit now through the main conduit, means forming an air discharge passage connecting the receptacle tor said main conveying conduit at a point vbeyond said diverter valve, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air 4flowing therethrough into said receptacle when said valve is in its diverting position, said discharge passage being eiective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, and means for exhausting air from the container free of conveyed material.

2. A pneumatic conveying system for delivering bulk flour or like material from a container to a remote destination, including a container from which the material may be drawn, a receptacle at the remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inletend at the container past said receptacle in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent the receptacle operative when the valve is in its diverting position to divert material from the main yconduit into the receptacle and in its straightthrough position to block communication between the main conduit and the receptacle and permit flow through the main conduit, means forming an air discharge passage connecting the receptacle to said main conveying conduit at a point beyond said diverter valve, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into said receptacle when said valve is in its diverting position, said discharge passage being effective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, means for exhausting air from the container free of conveyed material, means operable while material is being conveyed to said receptacle to shift said diverter valve to its straight-through position and thus terminate delivery of material to said receptacle, and means for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container aiter the diverter valve is returned to its straight-'through position.

3. A pneumatic conveying system for delivering bulk flour or like material from a container to a remote destination, including a container from which the material may be drawn, a receptacle at the remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacle in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent the receptacle operative when the valve is in its diverting position to divert material from the main conduit into the receptacle and in its straight-through position to block communication between the main conduit and the receptacle and permit iiow through the main conduit, means forming an air discharge passage connecting the receptacle to said main conveying conduit at a point beyond said diverter valve, means for preventing flow from the main conduit to the receptacle through the discharge passage when the diverter valve is in its straight-through position, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air iiowing therethrough into said receptacle when said valve is in its diverting position, said discharge passage being effective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, and means for exhausting air from the container free of conveyed material.

4. A pneumatic conveying system for delivering bulk flour or like material from a container to a remote destination, including a container from which the material may be drawn, a receptacle at the remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacle in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent the receptacle operative when the valve is in its diverting position to divert material from the main conduit into the receptacle and in its straightthrough position to block communication between the main conduit and the receptacle and permit now through the main conduit, means forming an air discharge passage connecting the receptacle to said main conveying conduit at a point beyond said diverter Valve, means for preventing flow from the main conduit to the receptacle through the discharge passage when the diverter valve is in its straight-through position, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into said receptacle when said valve is in its diverting position, said discharge passage being effective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, means for exhausting air from the container free of conveyed material, means operable while material is being conveyed to said receptacle to shift said divertervalve to its straight-through position and thus terminate delivery of material to said receptacle, and means for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned lto its straight-through position.

5. A pneumatic conveying system for delivering bulk flour or like material from a container to a remote destination, including a container from which the material may be drawn, a receptacle at the remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacle in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent the receptacle operative when the valve is in its diverting position to divert material from the main conduit into the receptacle and in its straightthrough position to block communication between the main conduit and the receptacle and permit flow through the main conduit, means forming an air discharge passage connecting the receptacle to said main conveying conduit at a point beyond said diverter valve, a check valve in said discharge passage for preventing reverse flow therein, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into said receptacle when said valve is in its diverting position, said discharge passage being effective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, and means for exhausting air from the container free of conveyed material.

6. A pneumatic conveying system for delivering bulk ilour or like material from a container to a remote destination, including a container from which the material may be drawn, a receptacle at the remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacle in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent the receptacle operative when the valve is in its diverting position to divert material from the main conduit into the receptacle and in its straight-through position to block communication between the main conduit and the receptacle and permit flow through the main conduit, means forming an air discharge passage connecting the receptacle to said main conveying conduit at a point beyond said diverter valve, a check valve in said discharge passage for preventing reverse ow therein, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into said receptacle when said valve is in its diverting position, said discharge passage being eiective to return to the container by Way of the remainder of the main conduit the air discharged by said receptacle, means for exhausting air from the container free of conveyed material, means operable while material is being conveyed to said receptacle to shift said diverter valve to its straight-through position and thus terminate delivery of material to said receptacle, and means for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned to its straight-through position.

'7. A pneumatic conveying system for delivering bulk flour or like material from a container to any one of a plurality of remote destinations, including a container from which the material may be drawn, a receptacle at each remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacles in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent each receptacle operative when the valve is in its diverting position to divert material from the main conduit 9 into.' the .associated receptacle and `in .its straightthrough position to block communication between .the main conduit and the yreceptacle and permit now 'through the main conduit, means forming a 'separate air discharge passage connecting each receptacle to `said main conveying conduit at a point beyond 'the associated Idiverter valve, means fior blowing air through the main conduit, means for 'feeding material from the container into the :main conduit at its inlet end for delivery by the fair owing therethrough into one of said receptacles when its diverter valve is in its diverting position, .said discharge passage being eiective to return to the container by way of the remainder vof the main conduit the air discharged by said receptacle, and means for exhausting air from the container free of conveyed material;

8. A pneumatic conveying system for delivering Vbulk flour or like material from a container to any one ofa plural-ity of remote destinations,

including a container from which the material lmay Ibe drawn, a receptacle at each remote ldestination for receiving the conveyed material and the conveying air, a main conveying conduit eX- ten'ding in a closed loop from its inlet end at the vilow through the main conduit, means forminga separate air discharge passage connecting each receptacle to said main conveying conduit at a point beyond the associated diverter valve, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into one of said receptacles when its diverter valve is in its diverting position, said discharge passage being efective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, means for exhausting air from the container free of conveyed material, means operable while material is being conveyed to one of said receptacles to shift said diverter valve to its straight-through. position and thus terminate delivery of material to said receptacle, and means for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned to its straight-through position.

9. A pneumatic conveying system for delivering bulls. flour or like material from a container to any one of a plurality of remote destinations, including a container from which the material may be drawn, a receptacle at cach remote destination for receiving the conveyed material and the conveying air, a main conveying conduit eX- tending in closed loop from its inlet end at the container past said receptacles in close proximity thereto returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent each receptacle operative when the valve is in its divert-r ing position to divert material fro:L the main conduit into the associated receptacle and in its straight-through position to block communication between the main conduit and the re` oeptacle and permit flow through the main conduit, means forming a separate air discharge passage connecting each receptacle to said main conveying conduit at a point beyond the associa-ted diverter valve, means for preventing flow from the main conduit to any receptacle through the associated discharge passage when the associated diverter valve is in its straight-through position, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into one of said receptacles when its diverter valve is in its diverting position, said discharge passage 'being effective to return to the container by way of the remainder of the main conduit the -air discharged by said receptacle, and means for exhausting air from the container free of conveyed material.

10. A pneumatic conveying system for delivering bulk flour or like material from a container to any one of a plurality of remote destinations, including a container from which vthe material may be drawn, a receptacle at each remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacles in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent each receptacle operative when the valve is in its diverting position to divert material from the main condu-it Vinto the associated receptacle and in its straight-through position to block communication between the main conduit and the receptacle and permit flow through the main conduit, means forming a separate air discharge passage connecting each receptacle to said main conveying conduit at a point beyond the associated diverter valve, means for preventing now from the main conduit to any receptacle through the associated discharge passage when the associated diverter valve is in its straight-through position, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into one of said receptacles when its diverter valve is in its diverting position, said discharge passage being eiiective to return to the container by Way of the remainder of the main conduit the air discharged by said receptacle, means for eX- hausting air from the container` free of conveyed material, means operable while material is being conveyed to one of said receptacles to shift said diverter valve to its straight-through position and thus terminate delivery of material to said receptacle, and means for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned to its straight-through position.

11. A pneumatic conveying system for delivering bulk flour or like material from a container to any one of a plurality of remote destinations, including a container from which the material may be drawn, a receptacle at each remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacles in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent each receptacle operative when the valve is in its diverting position to divert material from the main conduit into the associated receptacle and in its straight-through position to block communication between the main conduit and the receptacle and permit flow through the main conduit, means forming a separate air discharge passage connecting each receptacle to said main conveying conduit at a point beyond the associated diverter valve, a check valve in each discharge passage for preventing reverse flow therein, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into one of said receptacles when its diverter valve is in its diverting position, said discharge passage being effective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, and means for exhausting air from the container free of conveyed material.

12. A pneumatic conveying system for delivering bulk flour or like material from a con" tainer to any one of a plurality of remote destinations, including a container from which the material may be drawn, a receptacle at each remote destination for receiving the conveyed material and the conveying air, a main conveying conduit extending in a closed loop from its inlet end at the container past said receptacles in close proximity thereto and returning to the container at its discharge end, means including a diverter valve in the main conduit adjacent each receptacle operative when the valve is in its diverting position to divert material from the main conduit into the associated receptacle and in its straight-through position to block communication between the main conduit and. the receptacle and permit flow through the main conduit, means forming a separate air discharge passage connecting each receptacle to said main conveying conduit at a point beyond the associated diverter valve, a check valve in each discharge passage for preventing reverse flow therein, means for blowing air through the main conduit, means for feeding material from the container into the main conduit at its inlet end for delivery by the air flowing therethrough into one of said receptacles when its diverter valve is in its diverting position, said discharge passage being effective to return to the container by way of the remainder of the main conduit the air discharged by said receptacle, means for exhausting air from the container free of conveyed material, means operable while material is being conveyed to one of said receptacles to shift said diverter valve to its straight-through position and thus terminate delivery of material to said receptacle, and means for stopping the feed of material to the main conduit in order to permit the air blowing means to clear the main conduit by returning the material therein to the container after the diverter valve is returned to its straight-through position.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,248,851 Heisler Dec. 4, 1917 1,308,369 Renkin July 1, 1919 2,580,581 Niemitz Jan. 1, 1952 

